Removing Old Contact Paper from Windows

We moved into an apt that has old sticky contact paper on all the windows on the front porch. I have tried several things to get it off and nothing has worked. Does anyone have any suggestions? I've already smashed one window trying to scrape it off.

You could try wetting it with a spray bottle filled with diluted ammonia or straight white vinegar. Let it sit a bit to loosen the glue and then use a razor blade to scrape it off. This works well for a variety of stickers and sticker glue residue. Finish cleaning with rubbing alcohol to remove any remaining bits of glue.